<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style type="text/css">
		.myDiv {
			width: 300px;
			height: 300px;
			background-color: #333;
			margin: 0 auto;
		}
	</style>
</head>
<body>
	<div class="myDiv"></div>
</body>
</html>